With the reduction in voltage, it has become difficult to ensure stability of an SRAM cell. As an on-time of a word line becomes long, the number of cells that cause a disturb failure in which internal data is inverted at the time of reading is increased. On the other hand, if the on-time is shortened, the number of cells that cause a read failure due to read current shortage or a write failure tends to be large, so that both are in a trade-off relation.